PHILADELPHIA, Pennsylvania (CNN) -- Wendell Potter says he is finished defending the insurance industry, which he says is "beholden to Wall Street."

Wendell Potter once was a vice president in the public relations department for insurance giant Cigna.

At a hearing last week before the Senate Commerce Committee, the former vice president of corporate communications at the insurance giant Cigna testified, "I know from personal experience that members of Congress and the public have good reason to question the honesty and trustworthiness of the insurance industry."

The committee's chairman, Jay Rockefeller, D-West Virginia, told Potter, "You are better than Russell Crowe on 'The Insider,' " referring to the award-winning 1999 film about cigarette company executive Jeffrey Wigand, who blew the whistle on the tobacco industry's practices.

In his testimony and during an interview with CNN, Potter described how underwriters at his former company would drive small businesses with expensive insurance claims to dump their Cigna policies. Industry executives refer to the practice as "purging," Potter said.

"When that business comes up for renewal, the underwriters jack the rates up so much, the employer has no choice but to drop insurance," Potter said.

CNN obtained a transcript of a 2008 Cigna conference call with investors in which company executives use the term "purge."

But in an e-mail to CNN, Cigna spokesman Chris Curran denied the company engages in purging.

"We do not practice that. We will offer rates that are reflective of the competitive group health insurance market. We always encourage our clients to compare our proposed rates to those available from other carriers," Curran wrote.

Cigna had revenue of $19.1 billion in 2008, according to the company Web site.

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"It was almost like an electrical jolt," Potter said.

At the event, Potter took pictures of doctors offering free health care to the uninsured.

"The volunteer doctors were seeing patients in barns, people in animal stalls," Potter said. "It changed it for me."

He says he finally decided to quit in 2007 after Cigna's controversial handling of an insurance claim made by the family of a California teenager, Nataline Sarkysian.

The Sarkysian family made repeated appeals at news conferences for Cigna to approve a liver transplant for the 17-year-old, who had leukemia. Cigna initially declined to cover the operation, then reversed its decision.

Sarkysian died hours after the company's reversal.

As Cigna's spokesman during the controversy, Potter had no role in the decision to deny coverage. But he was inundated with angry phone calls.

"After she died, my voice mail and my e-mail inbox were just filled with messages from people who were just outraged, " Potter said.

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Now a senior fellow on health care for the nonpartisan watchdog group Center for Media and Democracy, Potter writes a blog on health care reform. In particular, he is keeping an eye on efforts to defeat legislation that would give Americans the option of joining a government health care plan, something he now supports.

He says he witnessed how the insurance industry torpedoed health care reform efforts during the Clinton administration.

"They conduct what I call duplicitous PR campaigns. They'll say what people want to hear," Potter says. "It's how they operate. You cannot trust these guys."

Potter is also taking aim at some of the TV commercials aired by groups opposed to changes. One such ad caught Potter's eye. Run by the conservative organization Patients United Now, the ad says that "now, Washington wants to bring Canadian-style health care to the U.S."

"Sometimes you'll see misleading information. And sometimes you'll see outright lies, like that [ad] is," Potter said, referring to the spot.

Patients United Now spokeswoman Amy Menefee disagreed.

"We're not saying there's a Canada health care act of 2009," Menefee said. "It is a trend. It's trending in that direction."

Potter notes that the leading proposals for health care in Congress do not seek to set up Canadian-style health care in the United States. He says claims that overhauling the system would lead to "rationing" of care are missing his point.

"What we have is rationing by corporate executives who are beholden to Wall Street. And it happens all the time," Potter said.